Control and delivery of high purity corrosive, toxic, oxidant, inert, pyrophoric fluids and mixtures of such fluids from fluid containers is necessary to a wide range of processing and manufacturing markets, such as in the medical and semiconductor industries. Use of such fluids can be hazardous, unless they are handled carefully.
An uncontrolled release of hazardous fluids is particularly undesirable for safety and toxicity reasons. Such a release can lead to catastrophic consequences, including injury and even death to persons working in the area where the fluid release occurs. In addition, in many industrial applications, any such release would also necessitate a partial or complete evacuation of, at least, the industrial facility in the area where the uncontrolled release occurred, resulting in substantial economic losses. An uncontrolled release also has the potential to cause costly damage to sensitive and expensive equipment exposed to such hazardous fluid, because many of these fluids are corrosive.
One type of arrangement for controlling hazardous fluids consists of a number of discrete components fitted to the outside of the fluid container valve to control such functions as pressure, flow, gas shut-off, and safety relief. Such an arrangement has numerous joints that are often prone to leakage, resulting in difficulty controlling the quality and purity of the fluid for the user's application. Often, at least some portion of such an arrangement must be enclosed in a gas cabinet. A gas cabinet is large and expensive. These prior arrangements utilizing discrete components, with their associated problems, are undesirable, particularly in processing and manufacturing applications where high purity corrosive, toxic, oxidant, inert, pyrophoric fluids and mixtures of such fluids are utilized, such as in the medical and semiconductor industries.
Another type of fluid control arrangement has been recently developed that can be used for, among other things, controlling hazardous fluids, and is disclosed by U.S. Pat. No. 6,314,986 B1 (“'986 patent”). The '986 patent is assigned to the assignee of the present invention, Air Products and Chemicals, Inc. As more particularly pointed out in the '986 patent, rather than just connecting a number of discrete components into a control panel system, which has also been proposed in some miniaturized gas control systems, the '986 patent encompasses redesigning and machining a group of components directly into a discrete body (referred to as a module), or onto an electronic chip (for example, in micro-electro-mechanical system units), such that a number of modules can be interconnected to meet various user and market needs.
The '986 patent discloses, among other things, building functions into the discrete body or module that can give users added benefits, such as direct pressure control and flow control, which may further permit the complete elimination of the gas cabinet. In addition, in the high technology, high cost markets, such as electronics, the '986 patent overcomes the problems associated with corrosion, contamination, and human exposure when making and breaking connections to the fluid container, especially when using high purity corrosive, toxic, oxidant, inert, or pyrophoric fluids and mixtures of such fluids.
Typically, these prior flow control arrangements have further employed fluid flow restrictors, such as restrictive flow orifices and capillary tubes, in view of the serious consequences that can result from an uncontrolled release of hazardous fluids. Fluid flow restrictors can be positioned in various locations in conventional valve systems.
The conventional restrictive flow orifice, for example, is a fluid flow restrictor employed for lowering the risk of catastrophic failure by reducing the mass flow release rate of fluid from the fluid container in the event of a system failure. Sometimes conventional restrictive flow orifices are placed upstream of any pressure regulation apparatus. Other times these conventional restrictive flow orifices are placed in the outlet of the fluid container valve, where such outlets typically have connections made according to Compressed Gas Association (CGA) standard V-1.
Conventional configuration of fluid flow restrictors, such as restrictive flow orifices, has been documented. For example, guidance on the conventional configuration of restrictive flow orifices is provided by the Semiconductor Equipment and Materials International (SEMI) Standards S5-93 and S5-0703. These SEMI Standards provide a safety guideline method for limiting the release of hazardous gases from a gas cylinder valve during transportation, storage and use. The SEMI Standards recommend that conventional flow limiting devices limit mass flow to a maximum allowable mass flow release rate based on full flow conditions, i.e. high tank pressures at 700 kilopascals (100 pounds per square inch gage) and higher. Other standards may contemplate maximum allowable mass flow rates based on higher or lower tank pressures depending on the user's application and the hazardous fluid used.
Standards, such as the SEMI standards, provide a method of configuring fluid flow restrictors based on a “worst-case” mass flow release rate. By using the “worst case” mass flow release rate, the fluid flow restrictor can be configured to limit mass flow to a maximum allowable mass flow release rate from a fluid container. Use of the “worst-case” mass flow release rate to configure the fluid flow restrictor means that the dimensions of the fluid flow path through the fluid flow restrictor are calculated using: a maximum fluid pressure of the fluid in the container, which is typically when the fluid container is at approximately its full capacity, the fluid density, and the allowable maximum mass flow release rate, which is usually dictated by safety regulations.
A fluid flow restrictor configured based on the “worst-case” release rate can have a number of disadvantages. Some of the disadvantages of configuring the conventional restrictive flow orifices based on the “worst case” mass flow release rate can be understood in the context of silane (SiH4) discharge from a fluid container. Silane is a spontaneously combustible gas and is recognized as having a high level of risk associated with its use requiring the highest level of risk mitigation for this gas.
One disadvantage is that, when the fluid container is filled with silane to the fill capacity of the fluid container, the resulting worst-case mass flow release rate of silane through a conventionally configured restrictive flow orifice normally will exceed the maximum allowable mass flow rate. One conventional practice to overcome this problem is to fill the fluid container to a lower pressure to satisfy the maximum allowable mass flow rate standard. Another practice is to put in a smaller restrictive flow orifice to limit the mass flow to the maximum allowable mass flow rate standard. Filling the fluid container with less fluid or using a smaller orifice is done at the price of added operational costs.
Another disadvantage of configuring a conventionally configured restrictive flow orifice based on the “worst case” mass flow release is that the contents of the fluid container cannot be fully utilized. For example, as silane is depleted from the fluid container, the delivery pressure steadily falls. Assuming that the silane flows at sonic velocity, the corresponding fall of the delivery pressure results in the maximum mass flow rate through the restrictive flow orifice dropping proportionally. At some point, the conventional cylinder valve system is no longer capable of supplying the fluid at a mass flow rate sufficient to meet the process demand. When such insufficient flow rate conditions occur, the conventional valve system must be taken off line, which wastes the remaining valuable gas that could not be utilized or withdrawn for the process application. Therefore, by not fully utilizing the fluid from the fluid container, the user incurs increased operational costs when using the conventional valve system.